1. Field of the Invention
The present invention is directed to polymer compositions. More particularly, it is directed to polymer compositions having good impact resistance and high transparency. Specifically, the the present invention is directed to a composition of polyparamethylstyrene and a styrene-butadiene block copolymer. This composition has been found to possess good impact resistance and high transparency.
2. Description of the Prior Art
Attempts to make highly transparent impact compositions have been made previously. For example, British Patent No. 1,230,507 by Wiley et al is directed to high impact monovinyl aromatic polymer compositions containing block copolymer. Essentially, a two component composition is disclosed. The first component forms 80 to 97 weight percent of the composition and is a monovinyl aromatic monomer containing up to 10 carbon atoms, present in the amount of at least 60 weight percent, and another monomer copolymerizable with the monovinyl aromatic monomer. The second component is a toughening agent, present in the amount of about 3 to 20 percent by weight. The toughening agent is formed from a block copolymer of a monovinyl aromatic monomer and 1,3-butadiene and optionally a rubbery butadiene polymer. There is no specific disclosure of the combination of polyparamethylstyrene and styrene-butadiene block copolymer.
Riess et al disclose blends of styrene polymer with mixtures of styrene-isoprene block copolymers in the Journal of Macromolecular Science and Physics, B17 (2) 355, 1980.
Although the composition specifically disclosed by Wiley et al show improved clarity over previous impact compositions, better clarity is desired.